Luggage scales can work well for weighing fish. These are electronic and portable and take 2 x AAA batteries. They are waterproof and weigh up to 40kg. They have a clear display with a blue background and are digital and have a choice of weighing units and it is very easy to toggle between them at the push of a button. They are black and has a soft rope to hold them with and a hook underneath which is made of steel so it is strong. It takes two batteries which are very easy to change when needed.